A File Delivery Table (FDT) file typically carried in a data stream in the art of data broadcast carries description information and Transport Object Identifiers (TOI) of respective files transmitted in the data stream, where a TOI identifies uniquely a file in a session. During reception of data files, a user equipment firstly receives and searches the file delivery table for a data file to be received and retrieves the TOI of the data file, and then receives IP packets from the broadcast stream according to the TOI and encapsulates them into a file.
In some data broadcast services, a broadcast data file is encrypted to secure the services, and the data file and a key file carrying a key are transmitted to a user. In order to enable a user equipment to retrieve the key to decrypt the data file upon reception of data broadcast, a mechanism is required in the data broadcast service to associate the data file and the key file carrying the key.
In view of this issue, an existing solution to a Multimedia Broadcast Multicast Service MBMS is as follows.
A data file in the MBMS service is encapsulated in the format of an OMA DRM DCF file, and an identifier of a key to decrypt the file is carried in a specific field (e.g., RightIssuerURL) of the DCF file. The key encrypting the file is encapsulated into a separate key file in the format of an MIKEY message, and an identifier of the encrypting key is carried in a specific field of the MIKEY message. The key file and the encrypted data file are transmitted in the same FLUTE stream.
A user equipment receives a data file in the following specific operations: 1. it firstly searches a file delivery table for a desired data file, retrieves a TOI value of the file and receives the data file according to the TOT value; 2. the user equipment parses the data file upon reception thereof and extracts a key identifier from the file; and 3. the user equipment receives all of key files, parses each of them, extracts a key identifier and a key therefrom and compares the key identifier with that in the data file, and if they are consistent, then it decrypts the data file using the key; otherwise, it continues with receiving a next key file.
In the prior art, a user equipment intended to receive only a specific data file has to receive all of key files and parses each of them until a corresponding key is retrieved and consequently has to receive a large amount of useless information and has its resource wasted; and also the user equipment fails to locate a desired key file rapidly and thus performs slow reception, a user's experience of a service may be degraded.